Steering of tracked vehicles such as crawlers used as bulldozers, military tanks, and the like is quite different from steering of wheeled vehicles such as automobiles. One cannot simply turn the "front wheels" on a tracked vehicle to effect steering. When the two tracks on a vehicle are driven at the same speed, the vehicle proceeds in a straight line. If one track is operated at a higher speed than the other track, the vehicle turns in the direction of the slower moving track with some sideways slippage of the tracks. The ultimate "steering" is when one track is driven forward and the other track is driven in the reverse direction, which may permit a vehicle to essentially turn on its own center. Such steering is not limited to tracked vehicles, but is sometimes used on short wheel base, highly maneuverable, wheeled vehicles and for some amphibious vehicles.
The ordinary way of steering a tracked vehicle employs a clutch and brakes on each track. To turn, the driver disengages the clutch on one track and may simultaneously brake that track, which jerks the vehicle toward the direction of the unpowered track. Such a system is simple and straightforward but requires a skilled operator to coordinate the clutching and braking to achieve the desired steering.
Modern military vehicles provide much smoother turning by employing separate automatic transmissions for each of the two tracks. Such automatic transmissions are large and costly, both to purchase and maintain.
An all-gear steerable transmission system has been proposed which is, in effect, two truck differentials back-to-back and suitably geared together. The principal driving power is applied to one differential and steering power is applied to the other differential. This technique is described in "All Gear Steering" by Michael Bargo, Jr., Popular Science, July 1985, pages 60 to 62.
It is significant that any steering system for a tracked vehicle be balanced, that is, it should be no harder to turn the vehicle in one direction than it is to turn the vehicle in the other direction.
Still further improvements can be made in all-gear drive systems for tracked vehicles. For example, by splitting the applied input power to two separate drive trains before steering, size and weight reductions can be made.